cleaning the engine while performing citric flush... Tach started working!
 

it's never worked since I got the car. my 82 SD, put the gauge cluster from the parts car 83 SD due to the 120mph speedo. (I hated the 85mph...) the tach did work in that car. anyway, the tach did not work in the 82, but since it was not my goal, I didn't worry about it much. well while I was chasing a warm running problem, I flushed and flushed to clear the motor, and I used the hose to cool down the motor between runs. anyway when I filled back up with the citric solution, my tach started working! it's a little flakey, at low speeds, so there may still be issues with the thing, but it's a tach! I have a tach!
I just love it when the car fixes itself, and also when fixing one thing makes other things work too!
oh, and the cruise control works now too.....

Where did you get your citric acid?

I recently did the citric acid flush and I would recommend it over any prestone or the likes. I looked hard for the stuff, the dealer said he could order it but I decided to look around. I finally found it at a health food store. 1 pound of the small crystals for 7 bucks.

I've been looking, too.....
 

I've been looking for Citric Acid also.....the Health Food Store was a great idea, I had not thought to look/ask there......:idea3:

SB

well since you are supposed to use 2.2 lbs for each flush, I decided getting it in 1 lb boxes would not do...(*I have 8 of these 617's, and SEVERAL other cars...) ebay sellers have 3, 5, 7, 17, 50, etc. Lb. boxes for sale, real reasonable. I got 17.5 for 37.97 delivered. just search for citric acid. it's also called bath bomb and fizzy powder
oh, and the car STILL will not stay under 100C... this is my second citric flush (man that cleans out everything) and I put in a german Tstat. do they make 160°F / 70°C tstats?

Have you tried a different temp gauge and sender? just a thought.
Thanks for the info above. Hmmmm, 2.2lbs.......

John,

FWIW: My 84 euro wagon ran hot (~100 C), had green coolant and was heavily scaled. I did the citric acid flush and replaced the thermostat (Behr, 80 C) and refilled with Zerex G-05. It still runs hot.

As I have started to drive the car more the temps are running less hot, despite the increasingly hot weather. Last night it was running at just over 90 C.

I still think there are bubbles in the system, but I'll be buying a new temp sender soon.

How did you cool the motor with the hose? My guess is your tach fix is temporary.

Have you taken any measurements at the tach amp? Pin #'s should be labeled on the socket. 2 is gnd, 6 is + 12V, 7&9 is mag pickup and should be around 80 ohms power off. 3 is output to tach. Wrap a short length of solid thin gauge wires around pins 3 and 2 of the tach amp, bring it out (tape up to make sure no shorts) and measure with a DVM on the AC scale. At 750 rpm idle, you should get between 0.2 to 0.4volts. This is the pulse output to the tach from the tach amp. If you get no voltage at all on pin 3, then possibly the mag pickup is bad, or the tach amp is bad, or wiring is bad, or the mag pickup gap is way off, or the single tooth (approx 1/8 dia 1/2 long) on the HB is missing..

I don't know, I filled the system really well, no chance there are bubbles in there. my next step is to pull the water pump, and change it, I will also replace the aluminum fan with a plastic one from an 85 D I have. that will get more air flow through there, but I will have to replace the alternator belts to do it... oh well.

oh, and I am shooting the head with my IR non contact thermometer, it is sitting right at 100C... so the temp sender is working right.

Try this T-stat
 

I have ordered a 74 degree t-stat from Autoparts Warehouse.com.

It is part number 116 200 00 15/G4001-15459 for a 450 SE.

I have heard that it will fit in the 617 engine. I am still waiting for it and willlet you know if it fits and makes a difference.

COOL! thanks man, I will wait for your experience to blossom.

The only other place I could find the citric acid was at a nusery, but they sold it in a 50lb bag for 65 bucks. I did not want to get into the citric acid selling business so I passed.
the guy at the nusery told me it is getting hard to find because I guess drug users use it for something, who knows.

I have been wondering about a cooler Tstat for my 96 also I would be curious to see it that one works for you. Mine is the 85C and is fully open at 94C

just choose your size... shipping is what gets you at ebay, some sellers are offering 2Lb. 12.00 free shipping... I have plenty of cars, so 17.5Lbs. was perfect for me. 22ish plus 10ish shipping.
http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=citric+acid&category0=

90*C is a good operating temperature !!
 

Your 80*C thermostat is controlling the coolant temperature entering the water pump for 80*C.....after the coolant circulates thru the engine and reaches the cylinder head....where the engine temperature sensor is located....a temperature of 90*C is good, it shows that you have increased the coolant 10*C as it flowed thru the entire engine.....

What a lot of folks don't seem to understand.....the thermostat on a Mercedes-Benz is not restricting coolant flow exiting the head to achieve it's desired temperature.....it is a mixing valve that takes hot coolant exiting the head and mixes it with the cooler coolant exiting the radiator to achieve a constant coolant temperature as it enters the engine.....there is a diagram of this in the MB Service Manual.....

This is the European viewpoint on cooling machinery.....which is pretty much the opposite of the way we think of it here in the USA....:rolleyes:

SB